It is known that modern engines are provided with a fuel injection system for directly injecting the fuel into the cylinders of the engine. The fuel injection system generally includes a fuel common rail and a plurality of electrically controlled fuel injectors, which are individually located in a respective cylinder of the engine and which are hydraulically connected to the fuel rail through dedicated injection lines.
The fuel injection control is a strategy of the engine management system, in order to ensure the engine performance in terms of available torque and reduced fuel consumption and emissions. Related to the present disclosure, the main strategies to compensate the fuel injection are: the so called “Cylinder Balancing” (CB), which performs cylinder-by-cylinder torque equalization, in other words makes sure that each injector delivers the same fuel quantity; the so called “End of line Injection Adjustment” (ETA), which compensates injectors spread at new; the Fuel Set-point Adaptation strategy (FSA), which compensate the injectors drift, during their lifetime. FSA strategy estimates the injection drift considering the intake air mass and the oxygen concentration in the exhaust gas and stores it in an adaptive map, defined in term of engine speed and fuel request.
In particular, the algorithm “Cylinder Balancing” helps the engine management system to maintain acceptable vibration, noise and emission levels during the vehicle lifetime, by means of a run-time balancing between the injectors fuel quantity. In other words, “Cylinder Balancing” purpose is the torque equalization of the mean effective pressure present in the combustion chamber, regardless the injectors drift, caused by the mileage accumulation and the injectors dispersion. The output of the “Cylinder Balancing” is an array of fuel corrections with respect to the nominal fuel, which is equal for all the cylinders.
The “Cylinder Balancing” strategy uses the crankshaft wheel signal, in particular the Electronic Control Unit receives as input the crankshaft angular accelerations related to each cylinder and a pure integral control calculates the fuel corrections to be applied to each cylinder. When an engine operating point change occurs, the “Cylinder Balancing strategy” has to converge again in the new operating point without any prediction term.
FIG. 3 shows a schematic of a known fuel injection control. A target injector fuel quantity (Qtarget) which has to be equal for all the injectors in the engine is corrected by an injector fuel quantity deviation (ΔQCB) which is estimated by the Cylinder Balancing algorithm. The corrected injector fuel quantity (Qcrtd) is then updated by taking into account the “End of line Injection Adjustment” and enters in the block 521, which calculates the injection parameters (injection pressure, energizing time) for each injector. Once the interactions between injectors and engine (i.e. the fuel injection and combustion) happen, a feedback signal is provided by the crank wheel in terms of instantaneous crankshaft angular accelerations, in other words in terms of maximum unbalanced torque (ΔM). The cylinder balancing routine then transforms the unbalanced torque in a delta fuel to be compensated to each injector, in order to let them inject the same fuel quantity.
In case of high rate engine operating point transients, for example, engine start (both after soaking and after automatic engine stop) or fuel cutoff and pedal tip-in, the “Cylinder Balancing” convergence could not be as fast as desired. Moreover, in case of much disturbed transmission gears (i.e. resonances due to coupling dual mass flywheel and transmission) or rough roads, the “Cylinder Balancing” feedback signal could not be so clean to balance the injectors as well as desired. Finally, in case of injectors, which are drifting all in one direction, the “Cylinder Balancing” does not correct the average drift.
Therefore, a need exists for a method that controls the fuel injection in an internal combustion engines, particularly related to the balance of the injection quantities for each cylinder, and is able to overcome the above problems.